Two options.

First of all in Memoize you can choose to have the cache be tied to a dbm on disk. That will allow your cache to grow on disk, which you probably have more of than RAM.

The other option to consider is to use the plug-in Memoize::Expire which allows you to set various kinds of expiration policies for your cache. Play around with that. I would suggest an expiration policy of once every X accesses where X is relatively large (eg a million or so). YMMV.